I base my Beech C23 at Bromont and I am a frequent visitor to CYSC (Sherbrooke), although my plane is grounded for the winter for maintenance. It should be back in the air in April.
You should be able to see airliners at fairly high altitude at YSC
. The Sherbrooke VOR (YSC
113.2) is directly under the V300 airway which is the main airway from Montreal to the Maritimes. The same airway passes just to the south of Bromont (CZBM) and in fact directly over my house (I've seen my house while on descent into Montreal on airline flights from the Maritimes). You would be seeing mainly A319s, A320s, CRJs, 737s and Dash 8s. Most westbound jet flights would be commencing their descents right around Sherbrooke or reaching TOC nearby as well. So they will be at fairly high altitudes.
Transatlantic flights tend to fly up the Saint Lawrence River as they track the Great Circle routes over the Pond.
Note that the Sherbrooke VOR is some distance to the south of the airport, and not near the airport itself, and is situated about 5 n.m. SE
of the city so the jet traffic would be passing just south of the city if on track.